The nuclear power industry, medical institutions, DOE facilities, and research and academic institutions generate a considerable quantity of low level dry radioactively contaminated trash (low level dry active waste) each year. A good percentage of this trash consists of plastic material or material which could be replaced by plastic. Such plastic material can include polyvinylchloride (PVC), polyethylene (PE), polypropylene, polystyrene and others. Polyvinylchloride and polyethylene are of particular interest due to their widespread use in the nuclear industry. Currently, such plastic material which is of a sufficiently low activity level is disposed of by shallow land burial i a controlled facility designed for such waste disposal. Such disposal facilities have become increasingly unpopular, and as a result of the strict regulations regarding the design and operation of such facilities, the cost of burial has escalated tremendously in recent years. Therefore, many strategies and techniques have been devised to incinerate, compact, or otherwise reduce the volume of material which must be disposed of at such low level waste burial facilities.
Plastic materials which are subject to becoming contaminated in the above environment range widely from clothing used to protect personnel, to cloths, drapes and coatings used to protect walls, floors, structures and equipment, and to actual structural elements and equipment.
The methods currently employed for reducing the volume of dry active waste include: (1) Compaction and Supercompaction, (2) Incineration, (3) Segregation, and (4) Miscellaneous washing or laundering processes.
The compaction and segregation processes attempt to physically reduce the volume of a given quantity of waste by the application of high pressure or by segregating individual pieces of the waste which can be identified as having an acceptably low level of radioactivity so as to be considered releasable to the environment.
The incineration process attempts to reduce the volume of waste by oxidizing all of the combustible components in the waste, thereby leaving a condensed and concentrated residue. The washing and laundering processes are used primarily for clothing materials as a method for reducing the contamination levels between uses. Some attempts have been made to launder plastic materials prior to disposal, however, these attempts have met with little success as regards to significant volume reduction.
Much knowledge of the characteristics of dry active waste is available in the literature. Characteristics which are of importance in devising a disposal method include (1) isotope composition, (2) particle size distribution, (3) soluble/insoluble proportions, and (4) chemical forms.
Due to the shipping and burial requirements for radioactive material, a great deal of isotopic distribution data is available in the literature. Although the numbers vary widely from year to year and from plant to plant, the predominant isotopes which account for the majority of the activity are Co-58 and Co-60 (Cobalt isotopes), Fe-55 (Iron isotopes), and Cs-134 and Cs-137 (Cesium isotopes). Cobalt-60 alone generally accounts for 40%-60% of the activity and is by far the most important contributor. Most of these isotopes are found in the form of salts and particulate oxides.
Further data shows that the particle size generally ranges from 0.1 to 5 microns. Of the identified isotopes the cobalt isotopes are generally insoluble while the cesium isotopes are generally soluble.